Slurry, and polishing method

ABSTRACT

A slurry containing abrasive grains and a liquid medium, in which the abrasive grains include first particles and second particles in contact with the first particles, a particle size of the second particles is smaller than a particle size of the first particles, the first particles contain cerium oxide, the second particles contain a cerium compound, and in a case where a content of the abrasive grains is 0.1% by mass, an absorbance for light having a wavelength of 380 nm in a liquid phase obtained when the slurry is subjected to centrifugal separation for 5 minutes at a centrifugal acceleration of 5.8×10 4  G exceeds 0.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national phase application filed under 35U.S.C. § 371 of International Application No. PCT/JP2019/028712, filedJul. 22, 2019, designating the United States, which claims priority fromInternational Application No. PCT/JP2018/028105, filed Jul. 26, 2018,which are hereby incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a slurry and a polishing method.

BACKGROUND ART

In the manufacturing steps for semiconductor elements of recent years,the importance of processing technologies for density increase andmicronization is increasing more and more. CMP (Chemical mechanicalpolishing) technology, which is one of the processing technologies, hasbecome an essential technology for the formation of a shallow trenchisolation (hereinafter, referred to as “STI”), flattening of a pre-metalinsulating material or an interlayer insulating material, formation of aplug or an embedded metal wiring, and the like in the manufacturingsteps for semiconductor elements.

Regarding polishing liquids that are most commonly used, for example,silica-based polishing liquids containing silica (silicon oxide)particles such as fumed silica and colloidal silica as abrasive grainsare mentioned. Silica-based polishing liquids have a feature of highflexibility of use, and by appropriately selecting the content ofabrasive grains, pH, additives, and the like, polishing of a widevariety of materials can be achieved regardless of whether the materialis an insulating material or an electroconductive material.

Meanwhile, as a polishing liquid mainly used for insulating materialssuch as silicon oxide, a demand for a polishing liquid containing ceriumcompound particles as abrasive grains is also increasing. For example, acerium oxide-based polishing liquid containing cerium oxide (ceria)particles as abrasive grains can polish silicon oxide at a high rateeven when the abrasive grain content is lower than that in thesilica-based polishing liquid (for example, see Patent Literatures 1 and2 described below).

Incidentally, in recent years, in the manufacturing steps forsemiconductor elements, it is required to achieve further micronizationof wiring, and polishing scratches generated at the time of polishingare becoming problematic. That is, when polishing is performed using aconventional cerium oxide-based polishing liquid, even if minutepolishing scratches are generated, there has been no problem as long asthe sizes of the polishing scratches are smaller than conventionalwiring widths; however, in a case where it is directed to achievefurther micronization of the wiring, even minute polishing scratchesbecome problematic.

With regard to this problem, an investigation has been conducted onpolishing liquids that use particles of cerium hydroxide (for example,see Patent Literatures 3 to 5 described below). Furthermore, methods forproducing particles of cerium hydroxide have also been investigated (forexample, see Patent Literatures 6 and 7 described below).

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Publication No.H10-106994

Patent Literature 2: Japanese Unexamined Patent Publication No.H08-022970

Patent Literature 3: International Publication WO 2002/067309

Patent Literature 4: International Publication WO 2012/070541

Patent Literature 5: International Publication WO 2012/070542

Patent Literature 6: Japanese Unexamined Patent Publication No.2006-249129

Patent Literature 7: International Publication WO 2012/070544

SUMMARY OF INVENTION Technical Problem

Incidentally, in recent years, 3D-NAND devices in which the cellportions of a device are laminated in the longitudinal direction havecome to the fore. In the present technology, the level differences ofthe insulating materials during cell formation are several times highercompared to the conventional planar types. According to this, in orderto maintain the throughput of the device production, it is necessary torapidly resolve the high level differences as described above in a CMPstep or the like, and it is necessary to improve the polishing rate foran insulating material.

The present invention is directed to solve the problems described above,and an object of the present invention is to provide a slurry capable ofimproving the polishing rate for an insulating material, and a polishingmethod using the slurry.

Solution to Problem

An aspect of a slurry of the present invention is a slurry containingabrasive grains and a liquid medium, in which the abrasive grainsinclude first particles and second particles in contact with the firstparticles, a particle size of the second particles is smaller than aparticle size of the first particles, the first particles contain ceriumoxide, the second particles contain a cerium compound, and in a casewhere a content of the abrasive grains is 0.1% by mass, an absorbancefor light having a wavelength of 380 nm in a liquid phase obtained whenthe slurry is subjected to centrifugal separation for 5 minutes at acentrifugal acceleration of 5.8×10⁴ G exceeds 0.

According to an aspect of the slurry of the present invention, it ispossible to improve the polishing rate for an insulating material, andtherefore, an insulating material can be polished at a high polishingrate.

An aspect of a polishing method of the present invention may include astep of polishing a surface to be polished by using the above-describedslurry. According to such a polishing method, the above-describedeffects similar to those obtainable with the above-described slurry canbe obtained by using the above-described slurry.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a slurrycapable of improving the polishing rate for an insulating material (forexample, silicon oxide). According to the present invention, a polishingmethod using the above-described slurry can be provided.

According to the present invention, it is possible to provide use of aslurry in polishing of a surface to be polished containing siliconoxide. According to the present invention, it is possible to provide useof a slurry in a flattening step of a base substrate surface that is themanufacturing technology of semiconductor elements. According to thepresent invention, it is possible to provide use of a slurry for aflattening step of an STI insulating material, a pre-metal insulatingmaterial, or an interlayer insulating material.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating a state in which abrasivegrains aggregate when an additive is added.

FIG. 2 is a schematic diagram illustrating a state in which abrasivegrains aggregate when an additive is added.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a slurry of embodiments of the present invention, and apolishing method using the slurry will be described in detail.

Definition

In the present specification, a numerical range that has been indicatedby use of “to” indicates the range that includes the numerical valueswhich are described before and after “to”, as the minimum value and themaximum value, respectively. In the numerical ranges that are describedstepwise in the present specification, the upper limit value or thelower limit value of the numerical range of a certain stage may bereplaced with the upper limit value or the lower limit value of thenumerical range of another stage. In the numerical ranges that aredescribed in the present specification, the upper limit value or thelower limit value of the numerical value range may be replaced with thevalue shown in the examples. “A or B” may include either one of A and B,and may also include both of A and B. Materials listed as examples inthe present specification can be used singly or in combinations of twoor more, unless otherwise specifically indicated. In the presentspecification, when a plurality of substances corresponding to eachcomponent exist in the composition, the content of each component in thecomposition means the total amount of the plurality of substances thatexist in the composition, unless otherwise specified.

As described later, a slurry of the present embodiment contains abrasivegrains. The abrasive grains are also referred to as “abrasiveparticles”; however, in the present specification, the term “abrasivegrains” is used. Abrasive grains are generally solid particles, and itis considered that at the time of polishing, an object to be removed isremoved by the mechanical action of the abrasive grains and the chemicalaction of the abrasive grains (mainly the surface of the abrasivegrains); however, it is not limited to this.

The weight average molecular weight in the present specification can bemeasured, for example, by a gel permeation chromatography method (GPC)under the following conditions using a calibration curve of standardpolystyrene.

Instrument used: Hitachi L-6000 Model [manufactured by Hitachi, Ltd.]

Column: Gel-Pak GL-R420+Gel-Pak GL-R430+Gel-Pak GL-R440 [manufactured byHitachi Chemical Co., Ltd., trade names, three columns in total]

Eluent: tetrahydrofuran

Measurement temperature: 40° C.

Flow rate: 1.75 mL/min

Detector: L-3300RI [manufactured by Hitachi, Ltd.]

<Slurry>

The slurry of the present embodiment contains abrasive grains and aliquid medium as essential components. The slurry of the presentembodiment can be used as, for example, a polishing liquid (CMPpolishing liquid). In the present specification, the term “polishingliquid” (abrasive) is defined as a composition to be brought intocontact with a surface to be polished, at the time of polishing. Theterm “polishing liquid” itself does not at all limit the components thatare contained in the polishing liquid.

The abrasive grains include composite particles including firstparticles and second particles in contact with the first particles. Theparticle size of the second particles is smaller than the particle sizeof the first particles. The first particles contain cerium oxide and thesecond particles contain a cerium compound. In a case where the contentof the abrasive grains is 0.1% by mass, the absorbance for light havinga wavelength of 380 nm in a liquid phase (supernatant solution) obtainedwhen the slurry of the present embodiment is subjected to centrifugalseparation for 5 minutes at a centrifugal acceleration of 5.8×10⁴ Gexceeds 0.

The polishing rate for an insulating material (for example, siliconoxide) can be improved by using the slurry of the present embodiment.The reasons why the polishing rate for an insulating material isimproved in this way are, for example, the reasons to be as follows.However, the reasons are not limited to the reasons to be as follows.

That is, the first particles containing cerium oxide and having a largerparticle size than that of the second particles have strong physicalaction (mechanical property) with respect to an insulating material ascompared to the second particles. On the other hand, the secondparticles containing a cerium compound and having a smaller particlesize than that of the first particles have small physical action withrespect to an insulating material as compared to the first particles,but have strong chemical action (chemical property) with respect to aninsulating material since the specific surface area (surface area perunit mass) in the whole particle is large. Therefore, a synergeticeffect of improving the polishing rate is easily obtained by using thefirst particles having strong physical action and the second particleshaving strong chemical action.

Further, in the slurry of the present embodiment, the absorbance forlight having a wavelength of 380 nm in a liquid phase obtained when theslurry is subjected to centrifugal separation exceeds 0. In suchcentrifugal separation, the composite particles are easy to beselectively removed, a liquid phase containing, as solid contents,particles that are free (hereinafter, referred to as “free particles”;for example, second particles not in contact with the first particles)can be obtained, and in a case where the absorbance exceeds 0, theabrasive grains include free particles in addition to the compositeparticles in the slurry. Since the free particles have a smallerparticle size than that of the composite particles, the free particleshave a high diffusion rate in the slurry and are preferentially adsorbedto a surface of an insulating material to coat the surface. In thiscase, as well as acting directly on the insulating material, thecomposite particles can act on the free particles adsorbed to theinsulating material to act indirectly on the insulating material (forexample, the physical action can be transferred to the insulatingmaterial through the free particles adsorbed to the insulatingmaterial).

As described above, by using the slurry of the present embodiment, it isspeculated that the polishing rate for an insulating material can beimproved.

The absorbance for light having a wavelength of 380 nm in a liquid phaseobtained when the slurry of the present embodiment is subjected tocentrifugal separation for 5 minutes at a centrifugal acceleration of5.8×10⁴ G is preferably in the following range. The absorbance ispreferably 0.001 or higher, more preferably 0.002 or higher, furtherpreferably 0.01 or higher, particularly preferably 0.03 or higher,extremely preferably 0.05 or higher, highly preferably 0.08 or higher,even more preferably 0.09 or higher, further preferably 0.1 or higher,and particularly preferably 0.2 or higher, from the viewpoint that thepolishing rate for an insulating material is further improved. In a casewhere the content of free particles in the slurry is large, it isspeculated that the amount of adsorption of free particles with respectto the insulating material is increased, and thus the polishing rate foran insulating material is further improved. The absorbance is preferably0.5 or less, more preferably 0.4 or less, further preferably 0.3 orless, particularly preferably 0.25 or less, and extremely preferably 0.2or less, from the viewpoint that the polishing rate for an insulatingmaterial is further improved. From the above-described viewpoints, theabsorbance is more preferably more than 0 and 0.5 or less. Theabove-described absorbance can be adjusted by adjusting the content offree particles in the abrasive grains. For example, the above-describedabsorbance can be decreased by increasing the surface area of the firstparticles with which the second particles are in contact, adjusting astate to an insufficient dispersion state when the first particles andthe second particles are brought into contact with each other (bydecreasing a dispersion time, decreasing the number of rotations instirring of a liquid containing the first particles and the secondparticles, weakening electrostatic repulsion generated betweenparticles, or the like), and the like.

(Abrasive Grains)

As described above, the abrasive grains of the slurry of the presentembodiment include free particles (for example, second particles not incontact with first particles) in addition to composite particlesincluding first particles and second particles in contact with the firstparticles. The particle size of the second particles is smaller than theparticle size of the first particles. The magnitude relationship inparticle size between the first particles and the second particles canbe determined from SEM images of the composite particles, or the like.

The particle size of the first particles is preferably in the followingrange. The lower limit of the particle size of the first particles ispreferably 15 nm or more, more preferably 25 nm or more, furtherpreferably 35 nm or more, particularly preferably 40 nm or more,extremely preferably 50 nm or more, highly preferably 80 nm or more, andeven more preferably 100 nm or more, from the viewpoint that thepolishing rate for an insulating material is further improved. The upperlimit of the particle size of the first particles is preferably 1000 nmor less, more preferably 800 nm or less, further preferably 600 nm orless, particularly preferably 400 nm or less, extremely preferably 300nm or less, highly preferably 200 nm or less, and even more preferably150 nm or less, from the viewpoint of improving the dispersibility ofthe abrasive grains and the viewpoint of easily suppressing scratches ata polished surface. From the above-described viewpoints, the particlesize of the first particles is more preferably 15 to 1000 nm. Theaverage particle size (average secondary particle size) of the firstparticles may be in the above ranges.

The particle size of the second particles is preferably in the followingrange. The lower limit of the particle size of the second particles ispreferably 1 nm or more, more preferably 2 nm or more, and furtherpreferably 3 nm or more, from the viewpoint that the polishing rate foran insulating material is further improved. The upper limit of theparticle size of the second particles is preferably 50 nm or less, morepreferably 30 nm or less, further preferably 25 nm or less, particularlypreferably 20 nm or less, extremely preferably 15 nm or less, and highlypreferably 10 nm or less, from the viewpoint of improving thedispersibility of the abrasive grains and the viewpoint of easilysuppressing scratches at a polished surface. From the above-describedviewpoints, the particle size of the second particles is more preferably1 to 50 nm. The average particle size (average secondary particle size)of the second particles may be in the above ranges.

The average particle size (average secondary particle size) of theabrasive grains (the entire abrasive grains including compositeparticles and free particles) in the slurry is preferably in thefollowing range.

The lower limit of the average particle size of the abrasive grains ispreferably 16 nm or more, more preferably 20 nm or more, furtherpreferably 30 nm or more, particularly preferably 40 nm or more,extremely preferably 50 nm or more, highly preferably 100 nm or more,even more preferably 120 nm or more, and further preferably 140 nm ormore, from the viewpoint that the polishing rate for an insulatingmaterial is further improved. The upper limit of the average particlesize of the abrasive grains is preferably 1050 nm or less, morepreferably 1000 nm or less, further preferably 800 nm or less,particularly preferably 600 nm or less, extremely preferably 500 nm orless, highly preferably 400 nm or less, even more preferably 300 nm orless, further preferably 200 nm or less, particularly preferably 160 nmor less, and extremely preferably 155 nm or less, from the viewpoint ofimproving the dispersibility of the abrasive grains and the viewpoint ofeasily suppressing scratches at a polished surface. From theabove-described viewpoints, the average particle size of the abrasivegrains is more preferably 16 to 1050 nm.

The average particle size can be measured, for example, using a lightdiffraction scattering type particle size distribution meter (forexample, trade name: N5 manufactured by Beckman Coulter, Inc. or tradename: MICROTRAC MT3300EXII manufactured by MicrotracBEL Corp.).

The first particles contain cerium oxide and the second particlescontain a cerium compound. Examples of the cerium compound of the secondparticles include cerium hydroxide and cerium oxide. As the ceriumcompound of the second particles, a compound different from cerium oxidecan be used. The cerium compound preferably contains cerium hydroxide.The abrasive grains containing cerium hydroxide have higher reactivity(chemical action) with an insulating material (for example, siliconoxide) by the action of the hydroxyl group than particles composed ofsilica, cerium oxide, or the like, and an insulating material can bepolished at a higher polishing rate. The cerium hydroxide is, forexample, a compound containing tetravalent cerium (Ce⁴⁺) and at leastone hydroxide ion (OH⁻). The cerium hydroxide may contain an anion (forexample, nitrate ion NO₃ ⁻ and sulfate ion SO₄ ²⁻) other than ahydroxide ion. For example, the cerium hydroxide may also contain ananion (for example, nitrate ion NO₃ ⁻ and sulfate ion SO₄ ²⁻) bonded totetravalent cerium. The abrasive grains may further include particlescomposed of silica, alumina, zirconia, yttria, or the like.

The cerium hydroxide can be prepared by reacting a cerium salt with analkali source (base). The cerium hydroxide is preferably prepared bymixing a cerium salt with an alkali liquid (for example, alkali aqueoussolution). Thereby, it is possible to obtain particles having anextremely fine particle size, and easily obtain a slurry excellent in aneffect of reducing polishing scratches. Such a technique is disclosedin, for example, Patent Literatures 6 and 7. The cerium hydroxide can beobtained by mixing a cerium salt solution (for example, a cerium saltaqueous solution) with alkali liquid. As the cerium salt, conventionallyknown salts can be used without any particular limitation, and examplesthereof include Ce(NO₃)₄, Ce(SO₄)₂, Ce(NH₄)₂(NO₃)₆, and Ce(NH₄)₄(SO₄)₄.

The composite particles including the first particles and the secondparticles can be obtained by bringing the first particles and the secondparticles into contact with each other using a homogenizer, a nanomizer,a ball mill, a bead mill, a sonicator, or the like; by bringing thefirst particles and the second particles each having opposing charges toeach other into contact with each other; by bringing the first particlesand the second particles into contact with each other in a state of asmall content of the particles; or the like.

The lower limit of the content of cerium oxide in the first particles ispreferably 50% by mass or more, more preferably 70% by mass or more,further preferably 90% by mass or more, and particularly preferably 95%by mass or more, on the basis of the entire first particles (the entirefirst particles contained in the slurry; the same applies hereinafter),from the viewpoint that the polishing rate for an insulating material isfurther improved. The first particles may be an embodiment substantiallycomposed of cerium oxide (an embodiment in which substantially 100% bymass of the first particles are cerium oxide).

The lower limit of the content of the cerium compound in the secondparticles is preferably 50% by mass or more, more preferably 70% by massor more, further preferably 90% by mass or more, and particularlypreferably 95% by mass or more, on the basis of the entire secondparticles (the entire second particles contained in the slurry; the sameapplies hereinafter), from the viewpoint that the polishing rate for aninsulating material is further improved. The second particles may be anembodiment substantially composed of a cerium compound (an embodiment inwhich substantially 100% by mass of the second particles are a ceriumcompound).

The content of the second particles can be estimated on the basis of avalue of absorbance of equation below which is obtained by aspectrophotometer when light having a specific wavelength is transmittedthrough the slurry. That is, in a case where particles absorb lighthaving a specific wavelength, the light transmittance of a regioncontaining these particles is decreased. The light transmittance isdecreased not only by absorption of the particles but also byscattering, but in the second particles, the influence of scattering issmall.

Therefore, in the present embodiment, the content of the secondparticles can be estimated on the basis of a value of absorbancecalculated by equation below.Absorbance=−LOG₁₀(Light transmittance [%]/100)

The lower limit of the content of the first particles in the abrasivegrains is preferably 50% by mass or more, more preferably more than 50%by mass, further preferably 60% by mass or more, particularly preferably70% by mass or more, extremely preferably 75% by mass or more, andhighly preferably 80% by mass or more, on the basis of the entireabrasive grains (the entire abrasive grains contained in the slurry; thesame applies hereinafter), from the viewpoint that the polishing ratefor an insulating material is further improved. The upper limit of thecontent of the first particles in the abrasive grains is preferably 95%by mass or less, more preferably 93% by mass or less, further preferably90% by mass or less, particularly preferably 88% by mass or less,extremely preferably 86% by mass or less, highly preferably 85% by massor less, and even more preferably 82% by mass or less, on the basis ofthe entire abrasive grains, from the viewpoint that the polishing ratefor an insulating material is further improved. From the above-describedviewpoints, the content of the first particles in the abrasive grains ismore preferably 50 to 95% by mass on the basis of the entire abrasivegrains.

The lower limit of the content of the second particles in the abrasivegrains is preferably 5% by mass or more, more preferably 7% by mass ormore, further preferably 10% by mass or more, particularly preferably12% by mass or more, extremely preferably 14% by mass or more, highlypreferably 15% by mass or more, and even more preferably 18% by mass ormore, on the basis of the entire abrasive grains (the entire abrasivegrains contained in the slurry), from the viewpoint that the polishingrate for an insulating material is further improved. The upper limit ofthe content of the second particles in the abrasive grains is preferably50% by mass or less, more preferably less than 50% by mass, furtherpreferably 40% by mass or less, particularly preferably 30% by mass orless, extremely preferably 25% by mass or less, and highly preferably20% by mass or less, on the basis of the entire abrasive grains, fromthe viewpoint that the polishing rate for an insulating material isfurther improved. From the above-described viewpoints, the content ofthe second particles in the abrasive grains is more preferably 5 to 50%by mass on the basis of the entire abrasive grains.

The lower limit of the content of cerium oxide in the abrasive grains ispreferably 50% by mass or more, more preferably more than 50% by mass,further preferably 60% by mass or more, particularly preferably 70% bymass or more, extremely preferably 75% by mass or more, and highlypreferably 80% by mass or more, on the basis of the entire abrasivegrains (the entire abrasive grains contained in the slurry), from theviewpoint that the polishing rate for an insulating material is furtherimproved. The upper limit of the content of cerium oxide in the abrasivegrains is preferably 95% by mass or less, more preferably 93% by mass orless, further preferably 90% by mass or less, particularly preferably88% by mass or less, extremely preferably 86% by mass or less, highlypreferably 85% by mass or less, and even more preferably 82% by mass orless, on the basis of the entire abrasive grains, from the viewpointthat the polishing rate for an insulating material is further improved.From the above-described viewpoints, the content of cerium oxide in theabrasive grains is more preferably 50 to 95% by mass on the basis of theentire abrasive grains.

The lower limit of the content of cerium hydroxide in the abrasivegrains is preferably 5% by mass or more, more preferably 7% by mass ormore, further preferably 10% by mass or more, particularly preferably12% by mass or more, extremely preferably 14% by mass or more, highlypreferably 15% by mass or more, and even more preferably 18% by mass ormore, on the basis of the entire abrasive grains (the entire abrasivegrains contained in the slurry), from the viewpoint that the polishingrate for an insulating material is further improved. The upper limit ofthe content of cerium hydroxide in the abrasive grains is preferably 50%by mass or less, more preferably less than 50% by mass, furtherpreferably 40% by mass or less, particularly preferably 30% by mass orless, extremely preferably 25% by mass or less, and highly preferably20% by mass or less, on the basis of the entire abrasive grains, fromthe viewpoint that the polishing rate for an insulating material isfurther improved. From the above-described viewpoints, the content ofcerium hydroxide in the abrasive grains is more preferably 5 to 50% bymass on the basis of the entire abrasive grains.

The lower limit of the content of the first particles is preferably 50%by mass or more, more preferably more than 50% by mass, furtherpreferably 60% by mass or more, particularly preferably 70% by mass ormore, extremely preferably 75% by mass or more, and highly preferably80% by mass or more, on the basis of the total amount of the firstparticles and the second particles, from the viewpoint that thepolishing rate for an insulating material is further improved. The upperlimit of the content of the first particles is preferably 95% by mass orless, more preferably 93% by mass or less, further preferably 90% bymass or less, particularly preferably 88% by mass or less, extremelypreferably 86% by mass or less, highly preferably 85% by mass or less,and even more preferably 82% by mass or less, on the basis of the totalamount of the first particles and the second particles, from theviewpoint that the polishing rate for an insulating material is furtherimproved. From the above-described viewpoints, the content of the firstparticles is more preferably 50 to 95% by mass on the basis of the totalamount of the first particles and the second particles.

The lower limit of the content of the second particles is preferably 5%by mass or more, more preferably 7% by mass or more, further preferably10% by mass or more, particularly preferably 12% by mass or more,extremely preferably 14% by mass or more, highly preferably 15% by massor more, and even more preferably 18% by mass or more, on the basis ofthe total amount of the first particles and the second particles, fromthe viewpoint that the polishing rate for an insulating material isfurther improved. The upper limit of the content of the second particlesis preferably 50% by mass or less, more preferably less than 50% bymass, further preferably 40% by mass or less, particularly preferably30% by mass or less, extremely preferably 25% by mass or less, andhighly preferably 20% by mass or less, on the basis of the total amountof the first particles and the second particles, from the viewpoint thatthe polishing rate for an insulating material is further improved. Fromthe above-described viewpoints, the content of the second particles ismore preferably 5 to 50% by mass on the basis of the total amount of thefirst particles and the second particles.

The lower limit of the content of the first particles in the slurry ispreferably 0.005% by mass or more, more preferably 0.008% by mass ormore, further preferably 0.01% by mass or more, particularly preferably0.05% by mass or more, extremely preferably 0.08% by mass or more, andhighly preferably 0.1% by mass or more, on the basis of the total massof the slurry, from the viewpoint that the polishing rate for aninsulating material is further improved. The upper limit of the contentof the first particles in the slurry is preferably 5% by mass or less,more preferably 3% by mass or less, further preferably 1% by mass orless, particularly preferably 0.5% by mass or less, and extremelypreferably 0.3% by mass or less, on the basis of the total mass of theslurry, from the viewpoint of enhancing the storage stability of theslurry. From the above-described viewpoints, the content of the firstparticles in the slurry is more preferably 0.005 to 5% by mass on thebasis of the total mass of the slurry.

The lower limit of the content of the second particles in the slurry ispreferably 0.005% by mass or more, more preferably 0.008% by mass ormore, further preferably 0.01% by mass or more, particularly preferably0.012% by mass or more, extremely preferably 0.015% by mass or more,highly preferably 0.018% by mass or more, even more preferably 0.02% bymass or more, further preferably 0.0225% by mass or more, andparticularly preferably 0.025% by mass or more, on the basis of thetotal mass of the slurry, from the viewpoint of further enhancing achemical interaction between the abrasive grains and a surface to bepolished so that the polishing rate for an insulating material isfurther improved. The upper limit of the content of the second particlesin the slurry is preferably 5% by mass or less, more preferably 3% bymass or less, further preferably 1% by mass or less, particularlypreferably 0.5% by mass or less, extremely preferably 0.1% by mass orless, highly preferably 0.05% by mass or less, even more preferably0.04% by mass or less, further preferably 0.035% by mass or less, andfurther preferably 0.03% by mass or less, on the basis of the total massof the slurry, from the viewpoints of easily avoiding the aggregation ofthe abrasive grains, and easily obtaining a more favorable chemicalinteraction between the abrasive grains and a surface to be polished toeasily utilize the properties of the abrasive grains effectively. Fromthe above-described viewpoints, the content of the second particles inthe slurry is more preferably 0.005 to 5% by mass on the basis of thetotal mass of the slurry.

The lower limit of the content of cerium oxide in the slurry ispreferably 0.005% by mass or more, more preferably 0.008% by mass ormore, further preferably 0.01% by mass or more, particularly preferably0.05% by mass or more, extremely preferably 0.08% by mass or more, andhighly preferably 0.1% by mass or more, on the basis of the total massof the slurry, from the viewpoint that the polishing rate for aninsulating material is further improved. The upper limit of the contentof cerium oxide in the slurry is preferably 5% by mass or less, morepreferably 3% by mass or less, further preferably 1% by mass or less,particularly preferably 0.5% by mass or less, and extremely preferably0.3% by mass or less, on the basis of the total mass of the slurry, fromthe viewpoint of enhancing the storage stability of the slurry. From theabove-described viewpoints, the content of cerium oxide in the slurry ismore preferably 0.005 to 5% by mass on the basis of the total mass ofthe slurry.

The lower limit of the content of cerium hydroxide in the slurry ispreferably 0.005% by mass or more, more preferably 0.008% by mass ormore, further preferably 0.01% by mass or more, particularly preferably0.012% by mass or more, extremely preferably 0.015% by mass or more,highly preferably 0.018% by mass or more, even more preferably 0.02% bymass or more, further preferably 0.0225% by mass or more, andparticularly preferably 0.025% by mass or more, on the basis of thetotal mass of the slurry, from the viewpoint of further enhancing achemical interaction between the abrasive grains and a surface to bepolished so that the polishing rate for an insulating material isfurther improved. The upper limit of the content of cerium hydroxide inthe slurry is preferably 5% by mass or less, more preferably 3% by massor less, further preferably 1% by mass or less, particularly preferably0.5% by mass or less, extremely preferably 0.1% by mass or less, highlypreferably 0.05% by mass or less, even more preferably 0.04% by mass orless, further preferably 0.035% by mass or less, and further preferably0.03% by mass or less, on the basis of the total mass of the slurry,from the viewpoints of easily avoiding the aggregation of the abrasivegrains, and easily obtaining a more favorable chemical interactionbetween the abrasive grains and a surface to be polished to easilyutilize the properties of the abrasive grains effectively. From theabove-described viewpoints, the content of cerium hydroxide in theslurry is more preferably 0.005 to 5% by mass on the basis of the totalmass of the slurry.

The lower limit of the content of the abrasive grains in the slurry ispreferably 0.01% by mass or more, more preferably 0.05% by mass or more,further preferably 0.1% by mass or more, particularly preferably 0.11%by mass or more, extremely preferably 0.113% by mass or more, highlypreferably 0.115% by mass or more, even more preferably 0.118% by massor more, further preferably 0.12% by mass or more, and particularlypreferably 0.125% by mass or more, on the basis of the total mass of theslurry, from the viewpoint that the polishing rate for an insulatingmaterial is further improved. The upper limit of the content of theabrasive grains in the slurry is preferably 10% by mass or less, morepreferably 5% by mass or less, further preferably 1% by mass or less,particularly preferably 0.5% by mass or less, extremely preferably 0.1%by mass or less, highly preferably 0.2% by mass or less, even morepreferably 0.15% by mass or less, further preferably 0.135% by mass orless, and particularly preferably 0.13% by mass or less, on the basis ofthe total mass of the slurry, from the viewpoint of enhancing thestorage stability of the slurry. From the above-described viewpoints,the content of the abrasive grains in the slurry is more preferably 0.01to 10% by mass on the basis of the total mass of the slurry.

The first particles can have a negative zeta potential. The secondparticles can have a positive zeta potential. The zeta potentialrepresents the surface potential of a particle. The zeta potential canbe measured, for example, using a dynamic light scattering type zetapotential measuring apparatus (for example, trade name: DelsaNano Cmanufactured by Beckman Coulter, Inc.). The zeta potential of theparticles can be adjusted using an additive. For example, by bringing amaterial having a carboxyl group (polyacrylic acid or the like) intocontact with particles containing cerium oxide, particles having anegative zeta potential can be obtained.

It is preferable that the second particles contain cerium hydroxidewhile satisfying at least one of the following conditions (a) and (b).Incidentally, an “aqueous dispersion liquid” having the content of thesecond particles adjusted to a predetermined amount means a liquidcontaining a predetermined amount of the second particles and water.

(a) The second particles provide an absorbance of 1.00 or higher forlight having a wavelength of 400 nm in an aqueous dispersion liquidhaving the content of the second particles adjusted to 1.0% by mass.

(b) The second particles provide an absorbance of 1.000 or higher forlight having a wavelength of 290 nm in an aqueous dispersion liquidhaving the content of the second particles adjusted to 0.0065% by mass.

With regard to the condition (a), by using particles that provide anabsorbance of 1.00 or higher for light having a wavelength of 400 nm inan aqueous dispersion liquid having the content of the second particlesadjusted to 1.0% by mass, the polishing rate can be further improved.The reasons for this are not necessarily clearly known; however, thepresent inventors speculate the reasons to be as follows. That is, it isconsidered that particles including Ce(OH)_(a)X_(b) (in the formula,a+b×c=4) composed of tetravalent cerium (Ce⁴⁺), one to three hydroxideions (OH⁻), and one to three anions (X^(c−)) are generated(incidentally, such particles are also “cerium hydroxide”) depending onproduction conditions of cerium hydroxide and the like. It is consideredthat, in Ce(OH)_(a)X_(b), an electron-withdrawing anion (X^(c−)) acts toenhance reactivity of the hydroxide ion and the polishing rate isimproved with the increase in abundance of Ce(OH)_(a)X_(b). Further, itis considered that, since particles containing Ce(OH)_(a)X_(b) absorbslight having a wavelength of 400 nm, the polishing rate is improvedalong with an increase in the abundance of Ce(OH)_(a)X_(b) forincreasing the absorbance for light having a wavelength of 400 nm.

It is considered that the particles containing cerium hydroxide cancontain not only Ce(OH)_(a)X_(b) but also Ce(OH)₄, CeO₂, or the like.Examples of the anions (X^(c−)) include NO₃ ⁻ and SO₄ ²⁻.

Incidentally, the containing of Ce(OH)_(a)X_(b) in the particlescontaining cerium hydroxide can be confirmed by a method for detecting apeak corresponding to the anions (X^(c−)) with FT-IR ATR method (Fouriertransform Infra Red Spectrometer Attenuated Total Reflection method)after washing the particles with pure water well. The existence of theanions (X^(c−)) can also be confirmed by XPS method (X-ray PhotoelectronSpectroscopy).

Here, it has been confirmed that an absorption peak at a wavelength of400 nm of Ce(OH)_(a)X_(b) (for example, Ce(OH)₃X) is much smaller thanthe below-mentioned absorption peak at a wavelength of 290 nm. In thisregard, the present inventors conducted an investigation on themagnitude of the absorbance using an aqueous dispersion liquid having acontent of 1.0% by mass, which has a relatively large content ofparticles and whose absorbance is likely to be detected to be high, andas a result, the present inventors found that an effect of improving thepolishing rate is excellent in the case of using particles having anabsorbance of 1.00 or higher for light having a wavelength of 400 nm inthe aqueous dispersion liquid.

The lower limit of the absorbance for light having a wavelength of 400nm is preferably 1.50 or higher, more preferably 1.55 or higher, andfurther preferably 1.60 or higher, from the viewpoint that it becomeseasier to polish an insulating material at a further excellent polishingrate.

With regard to the condition (b), by using second particles having anabsorbance of 1.000 or higher for light having a wavelength of 290 nm inan aqueous dispersion liquid having the content of the second particlesadjusted to 0.0065% by mass, the polishing rate can be further improved.The reasons for this are not necessarily clearly known; however, thepresent inventors speculate the reasons to be as follows. That is,particles containing Ce(OH)_(a)X_(b) (for example, Ce(OH)₃X), that areproduced depending on the production conditions for the cerium hydroxideand the like, have an absorption peak near the wavelength of 290 nmaccording to calculations, and for example, particles composed ofCe⁴⁺(OH⁻)₃NO₃ ⁻ have an absorption peak at the wavelength of 290 nm.Therefore, it is considered that, as the abundance of Ce(OH)_(a)X_(b)increases and thereby the absorbance for light having a wavelength of290 nm increases, the polishing rate is improved.

Here, the absorbance for light having a wavelength of about 290 nm tendsto be detected to a greater degree as the measuring limit is exceeded.In this regard, the present inventors conducted an investigation on themagnitude of the absorbance using an aqueous dispersion liquid having acontent of 0.0065% by mass, which has a relatively small content ofparticles and whose absorbance is easily detected to a small degree, andas a result, the present inventors found that the effect of improvingthe polishing rate is excellent in the case of using particles thatprovide an absorbance of 1.000 or higher for light having a wavelengthof 290 nm in the aqueous dispersion liquid.

The lower limit of the absorbance for light having a wavelength of 290nm is more preferably 1.050 or higher, further preferably 1.100 orhigher, particularly preferably 1.130 or higher, and extremelypreferably 1.150 or higher, from the viewpoint of polishing aninsulating material at a further excellent polishing rate. The upperlimit of the absorbance for light having a wavelength of 290 nm is notparticularly limited; however, for example, it is preferably 10.00 orlower.

In a case where the second particles, that provide an absorbance of 1.00or higher for light having a wavelength of 400 nm, provide an absorbanceof 1.000 or higher for light having a wavelength of 290 nm in an aqueousdispersion liquid having the content of the second particles adjusted to0.0065% by mass, an insulating material can be polished at a furtherexcellent polishing rate.

Furthermore, cerium hydroxide (for example, Ce(OH)_(a)X_(b)) tends notto absorb light having a wavelength of 450 nm or higher (particularly, awavelength of 450 to 600 nm). Therefore, from the viewpoint ofsuppressing adverse influence on polishing as a result of containingimpurities, and thereby polishing an insulating material at a furtherexcellent polishing rate, it is preferable that the second particlesprovide an absorbance of 0.010 or lower for light having a wavelength of450 to 600 nm in an aqueous dispersion liquid having the content of thesecond particles adjusted to 0.0065% by mass (65 ppm). That is, it ispreferable that the absorbance for entire light in the wavelength rangeof 450 to 600 nm in an aqueous dispersion liquid having the content ofthe second particles adjusted to 0.0065% by mass does not exceed 0.010.The upper limit of the absorbance for light having a wavelength of 450to 600 nm is more preferably lower than 0.010. The lower limit of theabsorbance for light having a wavelength of 450 to 600 nm is preferably0.

The absorbance in an aqueous dispersion liquid can be measured using,for example, a spectrophotometer (device name: U3310) manufactured byHitachi, Ltd. Specifically, for example, an aqueous dispersion liquidhaving the content of the second particles adjusted to 1.0% by mass or0.0065% by mass is prepared as a measuring sample. About 4 mL of thismeasuring sample is introduced into a 1-cm square cell, and the cell isplaced in the device. Next, measurement of the absorbance is performedin the wavelength range of 200 to 600 nm, and the absorbance isdetermined from a chart thus obtained.

It is preferable that the second particles contained in the slurry ofthe present embodiment provide a light transmittance of 50%/cm or morefor light having a wavelength of 500 nm in an aqueous dispersion liquidhaving the content of the second particles adjusted to 1.0% by mass.Thereby, a decrease in the polishing rate due to the addition of anadditive can be further suppressed, and therefore, it becomes easy toobtain other characteristics while maintaining the polishing rate. Fromthis viewpoint, the lower limit of the light transmittance is morepreferably 60%/cm or more, further preferably 70%/cm or more,particularly preferably 80%/cm or more, extremely preferably 90%/cm ormore, and highly preferably 92%/cm or more. The upper limit of the lighttransmittance is 100%/cm.

The reason why it is possible to suppress a decrease in the polishingrate by adjusting the light transmittance of the second particles likethis is not understood in detail; however, the present inventorsconsider the reason as follows. It is considered that, in particlescontaining cerium hydroxide, chemical action becomes predominant overmechanical action. Therefore, it is considered that the number ofparticles contributes to the polishing rate rather than the size of theparticles.

In a case where the light transmittance of an aqueous dispersion liquidhaving a content of particles of 1.0% by mass is low, it is consideredthat the particles present in the aqueous dispersion liquid contain arelatively larger portion of particles having a large particle size(hereinafter, referred to as “coarse particles”). When an additive (forexample, polyvinyl alcohol (PVA)) is added to a slurry containing suchparticles, as illustrated in FIG. 1 , coarse particles serve as nuclei,and other particles aggregate around thereon. As a result, it isconsidered that, since the number of particles acting on the surface tobe polished per unit area (effective number of particles) is reduced,and the specific surface area of the particles that are in contact withthe surface to be polished is reduced, a decrease in the polishing rateis induced.

On the other hand, in a case where the light transmittance in an aqueousdispersion liquid having a content of particles of 1.0% by mass is high,it is considered that the particles present in the aqueous dispersionliquid are in a state in which there are few “coarse particles”. In acase where the abundance of coarse particles is small like this, asillustrated in FIG. 2 , even if an additive (for example, polyvinylalcohol) is added to the slurry, since there are few coarse particlesthat become the nuclei of aggregation, aggregation between particles issuppressed, or the size of the aggregated particles becomes smallercompared to the aggregated particles illustrated in FIG. 1 . As aresult, it is considered that, since the number of particles acting onthe surface to be polished per unit area (effective number of particles)is maintained, and the specific surface area of the particles that arein contact with the surface to be polished is maintained, a decrease inthe polishing rate does not easily occur.

According to the investigation of the present inventors, it can be seenthat, even for slurries having the same particle size measured with ageneral particle size analyzer, there may be a slurry that is visuallytransparent (the light transmittance is high) and a slurry that isvisually cloudy (the light transmittance is low). From this, it isconsidered that coarse particles that can cause such action as describedabove contribute to a decrease in the polishing rate even with a verysmall amount that is undetectable with a general particle size analyzer.

Furthermore, it can be seen that, even if filtration is repeated severaltimes in order to reduce coarse particles, the occurrence that thepolishing rate is decreased by an additive is not much ameliorated, andthe above-described effect of improving the polishing rate due to theabsorbance may not be sufficiently exhibited. Thus, the presentinventors found that the above-described problems can be solved bydevising the production method for particles or the like and usingparticles having a high light transmittance in an aqueous dispersionliquid.

The light transmittance can be measured with a spectrophotometer.Specifically, for example, it can be measured with a spectrophotometerU3310 manufactured by Hitachi, Ltd.

As a more specific measurement method, an aqueous dispersion liquidhaving the content of the second particles adjusted to 1.0% by mass isprepared as a measuring sample. About 4 mL of this measuring sample isintroduced into a 1-cm square cell, the cell is placed in the device,and then measurement is performed.

The absorbance and light transmittance that are provided in the aqueousdispersion liquid by the second particles contained in the slurry can bemeasured by removing solid components other than the second particlesand liquid components other than water, subsequently preparing anaqueous dispersion liquid having a predetermined content, and performingmeasurement using this aqueous dispersion liquid. It may vary dependingon the components contained in the slurry; however, for the removal ofsolid components or liquid components, for example, a centrifugationmethod such as centrifugation using a centrifuge that can apply agravitational acceleration of several thousand G or less, orsuper-centrifugation using a super-centrifuge that can apply agravitational acceleration of several ten thousand G or greater; achromatographic method such as partition chromatography, adsorptionchromatography, gel permeation chromatography, or ion exchangechromatography; a filtration method such as natural filtration,filtration under reduced pressure, pressure filtration, orultrafiltration; and a distillation method such as reduced pressuredistillation or normal pressure distillation, can be used, and these mayalso be used in combination as appropriate.

For example, in a case where a compound having a weight averagemolecular weight of several ten thousands or more (for example, 50000 ormore) is contained, examples of a separation method for the secondparticles include a chromatographic method and a filtration method, andamong these, at least one selected from the group consisting of gelpermeation chromatography and ultrafiltration is preferred. In the caseof using a filtration method, the particles contained in the slurry canbe passed through a filter by setting appropriate conditions. In a casewhere a compound having a weight average molecular weight of several tenthousands or less (for example, less than 50000) is contained, examplesof the separation method for the second particles include achromatographic method, a filtration method, and a distillation method,and at least one selected from the group consisting of gel permeationchromatography, ultrafiltration, and distillation under reduced pressureis preferred. In a case where a plurality of kinds of particles arecontained, examples of the separation method for the second particlesinclude a filtration method and a centrifugation method, and moreparticles containing cerium hydroxide are contained in the filtrate inthe case of filtration, while more particles are contained in the liquidphase in the case of centrifugation.

As a method of separating solid components other than the secondparticles, for example, it is possible to separate under the followingconditions for centrifugation.

Centrifugal separator: Optima MAX-TL (manufactured by Beckman Coulter,Inc.)

Centrifugal acceleration: 5.8×10⁴ G

Treatment time: 5 minutes

Treatment temperature: 25° C.

As a method of separating the second particles by a chromatographicmethod, for example, it is possible to isolate the second particlesand/or other components under the following conditions.

Sample solution: 100 μL of slurry

Detector: Manufactured by Hitachi, Ltd., UV-VIS detector, trade name“L-4200”

Wavelength: 400 nm

Integrator: Manufactured by Hitachi, Ltd., GPC integrator, trade name“D-2500”

Pump: Manufactured by Hitachi, Ltd., trade name “L-7100”

Column: Manufactured by Hitachi Chemical Co., Ltd., water-based packedcolumn for HPLC, trade name “GL-W550S”

Eluent: Deionized water

Measurement temperature: 23° C.

Flow rate: 1 mL/min (pressure is about 40 to 50 kg/cm²)

Measurement time: 60 minutes

Depending on the components contained in the slurry, there is apossibility that the second particles may not be isolated even under theabove-described conditions; however, in that case, it is possible toseparate by optimizing the amount of the sample solution, the type ofcolumn, the type of eluent, the measurement temperature, the flow rate,and the like. Furthermore, there is a possibility that it is possible toseparate from the second particles by adjusting the pH of the slurry toadjust the distillation time for the components contained in the slurry.In a case where there are insoluble components in the slurry, it ispreferable to remove the insoluble components by filtration,centrifugation, and the like, according to necessity.

(Liquid Medium)

The liquid medium is not particularly limited; however, water such asdeionized water or ultrapure water is preferred. The content of theliquid medium may be the balance of the slurry remaining after excludingthe contents of other constituent components, and the content is notparticularly limited.

(Optional Components)

The slurry of the present embodiment may further contain optionaladditives for the purpose of adjusting the polishing characteristics,and the like. Examples of the optional additives include a materialhaving a carboxyl group (excluding a compound corresponding to apolyoxyalkylene compound or a water-soluble polymer), a polyoxyalkylenecompound, a water-soluble polymer, an oxidizing agent (for example,hydrogen peroxide), and a dispersant (for example, a phosphoricacid-based inorganic salt). The respective additives can be used singlyor in combination of two or more kinds thereof.

Optional additives (a water-soluble polymer or the like) have an effectby which the dispersion stability of the abrasive grains in the slurrycan be enhanced, and an insulating material (for example, silicon oxide)can be polished at a higher rate. Furthermore, since an insulatingmaterial (for example, silicon oxide) can be polished at a high rate,the level difference elimination property is improved, and highflattening properties can also be obtained. This is considered to bebecause the polishing rate for convex portions is improved to a largeextent compared to concave portions.

Examples of the material having a carboxyl group include monocarboxylicacids such as acetic acid, propionic acid, butyric acid, and valericacid; hydroxy acids such as lactic acid, malic acid, and citric acid;dicarboxylic acids such as malonic acid, succinic acid, fumaric acid,and maleic acid; polycarboxylic acids such as polyacrylic acid andpolymaleic acid; and amino acids such as arginine, histidine, andlysine.

Examples of the polyoxyalkylene compound include a polyalkylene glycoland a polyoxyalkylene derivative.

Examples of the polyalkylene glycol include polyethylene glycol,polypropylene glycol, and polybutylene glycol. The polyalkylene glycolis preferably at least one selected from the group consisting ofpolyethylene glycol and polypropylene glycol, and is more preferablypolyethylene glycol.

A polyoxyalkylene derivative is, for example, a compound obtained byintroducing a functional group or a substituent to a polyalkyleneglycol, or a compound obtained by adding a polyalkylene oxide to anorganic compound. Examples of the functional group or a substituentinclude an alkyl ether group, an alkyl phenyl ether group, a phenylether group, a styrenated phenyl ether group, a glyceryl ether group, analkylamine group, a fatty acid ester group, and a glycol ester group.Examples of the polyoxyalkylene derivative include a polyoxyethylenealkyl ether, polyoxyethylene bisphenol ether (for example, manufacturedby NIPPON NYUKAZAI CO., LTD., BA GLYCOL series), polyoxyethylenestyrenated phenyl ether (for example, manufactured by Kao Corporation,EMULGEN series), a polyoxyethylene alkyl phenyl ether (for example,manufactured by DKS Co. Ltd., NOIGEN EA series), a polyoxyalkylenepolyglyceryl ether (for example, manufactured by Sakamoto Yakuhin KogyoCo., Ltd., SC-E series and SC-P series), a polyoxyethylene sorbitanfatty acid ester (for example, manufactured by DKS Co. Ltd., SORGEN TWseries), a polyoxyethylene fatty acid ester (for example, manufacturedby Kao Corporation, EMANON series), a polyoxyethylene alkylamine (forexample, manufactured by DKS Co. Ltd., AMIRADIN D), and other compoundshaving a polyalkylene oxide added thereto (for example, manufactured byNissin Chemical Co., Ltd., SURFINOL 465, and manufactured by NIPPONNYUKAZAI CO., LTD., TMP series).

A water-soluble polymer has an effect of adjusting the polishingcharacteristics such as the dispersion stability of the abrasive grains,flattening properties, in-plane uniformity, polishing selectivity forsilicon oxide with respect to silicon nitride (polishing rate forsilicon oxide/polishing rate for silicon nitride), and polishingselectivity for silicon oxide with respect to polysilicon (polishingrate for silicon oxide/polishing rate for polysilicon). Here, the“water-soluble polymer” is defined as a polymer which is dissolved in100 g of water in an amount of 0.1 g or more. Incidentally, a polymerthat corresponds to the polyoxyalkylene compound is not to be includedin the “water-soluble polymer”.

The water-soluble polymer is not particularly limited, and examplesinclude acrylic polymers such as polyacrylamide andpolydimethylacrylamide; polysaccharides such as carboxymethyl cellulose,agar, curdlan, dextrin, cyclodextrin, and pullulan; vinyl-based polymerssuch as polyvinyl alcohol, polyvinylpyrrolidone, and polyacrolein;glycerin-based polymers such as polyglycerin and a polyglycerinderivative; and polyethylene glycol.

In the case of using a water-soluble polymer, the lower limit of thecontent of the water-soluble polymer is preferably 0.001% by mass ormore, more preferably 0.01% by mass or more, further preferably 0.1% bymass or more, particularly preferably 0.3% by mass or more, andextremely preferably 0.5% by mass or more, on the basis of the totalmass of the slurry, from the viewpoint that an effect of adding awater-soluble polymer is obtained while sedimentation of the abrasivegrains is suppressed. The upper limit of the content of thewater-soluble polymer is preferably 10% by mass or less, more preferably8% by mass or less, further preferably 6% by mass or less, particularlypreferably 5% by mass or less, extremely preferably 3% by mass or less,and highly preferably 1% by mass or less, on the basis of the total massof the slurry, from the viewpoint that an effect of adding awater-soluble polymer is obtained while sedimentation of the abrasivegrains is suppressed.

(Characteristics of Slurry)

The light transmittance for light having a wavelength of 500 nm in aliquid phase obtained when the slurry of the present embodiment issubjected to centrifugal separation for 5 minutes at a centrifugalacceleration of 5.8×10⁴ G is preferably 50%/cm or more, more preferably60%/cm or more, further preferably 70%/cm or more, particularlypreferably 80%/cm or more, extremely preferably 90%/cm or more, andhighly preferably 92%/cm or more, from the viewpoint that the polishingrate for an insulating material is further improved. The upper limit ofthe light transmittance is 100%/cm.

The lower limit of the pH of the slurry of the present embodiment ispreferably 2.0 or more, more preferably 2.5 or more, further preferably2.8 or more, particularly preferably 3.0 or more, extremely preferably3.2 or more, highly preferably 3.5 or more, even more preferably 4.0 ormore, further preferably 4.2 or more, and particularly preferably 4.3 ormore, from the viewpoint that the polishing rate for an insulatingmaterial is further improved. The upper limit of the pH is preferably7.0 or less, more preferably 6.5 or less, further preferably 6.0 orless, particularly preferably 5.0 or less, extremely preferably 4.8 orless, highly preferably 4.7 or less, even more preferably 4.6 or less,further preferably 4.5 or less, and particularly preferably 4.4 or less,from the viewpoint that the storage stability of the slurry is furtherimproved. From the above-described viewpoints, the pH is more preferably2.0 to 7.0. The pH of the slurry is defined as the pH at a liquidtemperature of 25° C.

The pH of the slurry can be adjusted by means of an acid component suchas an inorganic acid or an organic acid; an alkali component such asammonia, sodium hydroxide, tetramethylammonium hydroxide (TMAH),imidazole, or an alkanolamine; or the like. Furthermore, a bufferingagent may be added in order to stabilize the pH. Furthermore, abuffering agent may be added as a buffer solution (a liquid containing abuffering agent). Examples of such a buffer solution include an acetatebuffer solution and a phthalate buffer solution.

The pH of the slurry of the present embodiment can be measured by a pHmeter (for example, Model No. PHL-40 manufactured by DKK-TOACORPORATION). Specifically, for example, a pH meter is subjected totwo-point calibration using a phthalate pH buffer solution (pH: 4.01)and a neutral phosphate pH buffer solution (pH: 6.86) as standard buffersolutions, subsequently the electrode of the pH meter is introduced intothe slurry, and the value after being stabilized after a lapse of twominutes or longer is measured. The liquid temperatures of the standardbuffer solutions and the slurry are all set to 25° C.

In a case where the slurry of the present embodiment is used as a CMPpolishing liquid, the constituent components of the polishing liquid maybe stored as a one-pack polishing liquid, or may be stored as amulti-pack (for example, two-pack) polishing liquid set in which theconstituent components of the polishing liquid are divided into a slurryand an additive liquid such that a slurry (first liquid) containingabrasive grains and a liquid medium, and an additive liquid (secondliquid) containing additives and a liquid medium are mixed to form thepolishing liquid. The additive liquid may contain, for example, anoxidizing agent. The constituent components of the polishing liquid maybe stored as a polishing liquid set divided into three or more liquids.

In the polishing liquid set, the slurry and the additive liquid aremixed immediately before polishing or during polishing to prepare thepolishing liquid. Furthermore, a one-pack polishing liquid may be storedas a stock solution for a polishing liquid with a reduced liquid mediumcontent and used by dilution with a liquid medium at the time ofpolishing. A multi-pack polishing liquid set may be stored as a stocksolution for a slurry and a stock solution for an additive liquid withreduced liquid medium contents, and used by dilution with a liquidmedium at the time of polishing.

<Polishing Method>

The polishing method of the present embodiment (such as a polishingmethod of a base substrate) includes a polishing step of polishing asurface to be polished (such as a surface to be polished of a basesubstrate) by using the slurry. The slurry in the polishing step may bea polishing liquid obtained by mixing the slurry and the additive liquidof the above-described polishing liquid set.

In the polishing step, for example, in a state where a material to bepolished of the base substrate that has the material to be polished ispressed against a polishing pad (polishing cloth) of a polishing platen,the slurry is supplied between the material to be polished and thepolishing pad, and the base substrate and the polishing platen are movedrelative to each other to polish the surface to be polished of thematerial to be polished. In the polishing step, for example, at least apart of a material to be polished is removed by polishing.

As the base substrate that is to be polished, a substrate to be polishedor the like is exemplified. As the substrate to be polished, forexample, a base substrate in which a material to be polished is formedon a substrate for semiconductor element production (for example, asemiconductor substrate in which an STI pattern, a gate pattern, awiring pattern, or the like is formed) is exemplified. Examples of thematerial to be polished include an insulating material such as siliconoxide. The material to be polished may be a single material or aplurality of materials. In a case where a plurality of materials areexposed on a surface to be polished, they can be considered as amaterial to be polished. The material to be polished may be in the formof a film (film to be polished) or may be an insulating film such as asilicon oxide film.

By polishing a material to be polished (for example, an insulatingmaterial such as silicon oxide) formed on such a substrate with theslurry and removing an excess part, it is possible to eliminateirregularities on the surface of a material to be polished and toproduce a smooth surface over the entire surface of the polishedmaterial.

In the polishing method of the present embodiment, as a polishingapparatus, it is possible to use a common polishing apparatus which hasa holder capable of holding a base substrate having a surface to bepolished and a polishing platen to which a polishing pad can be pasted.A motor or the like in which the number of rotations can be changed isattached to each of the holder and the polishing platen. As thepolishing apparatus, for example, polishing apparatus: F-REX300manufactured by EBARA CORPORATION, or polishing apparatus: MIRRAmanufactured by Applied Materials, Inc. can be used.

As the polishing pad, common unwoven cloth, a foamed body, an unfoamedbody, and the like can be used. As the material for the polishing pad,it is possible to use a resin such as polyurethane, an acrylic resin,polyester, an acrylic-ester copolymer, polytetrafluoroethylene,polypropylene, polyethylene, poly-4-methylpentene, cellulose, celluloseester, polyamide (for example, Nylon (trade name) and aramid),polyimide, polyimidamide, a polysiloxane copolymer, an oxirane compound,a phenolic resin, polystyrene, polycarbonate, or an epoxy resin.Particularly, from the viewpoint of obtaining further excellentpolishing rate and flattening properties, the material for the polishingpad is preferably at least one selected from the group consisting of afoamed polyurethane and a non-foamed polyurethane. It is preferable thatthe polishing pad is subjected to groove processing, by which the slurryaccumulates thereon.

Polishing conditions are not limited, but the upper limit of therotation speed of a polishing platen is preferably 200 min′ (min′=rpm)or less such that the base substrate is not let out, and the upper limitof the polishing pressure to be applied to the base substrate(processing load) is preferably 100 kPa or less from the viewpoint ofeasily suppressing the generation of polishing scratches. The slurry ispreferably continuously supplied to the polishing pad with a pump or thelike during polishing. There are no limitations on the supply amount forthis, however, it is preferable that the surface of the polishing pad isalways covered with the slurry.

The slurry and the polishing method of the present embodiment arepreferably used for polishing a surface to be polished containingsilicon oxide. The slurry and the polishing method of the presentembodiment can be suitably used in formation of an STI and polishing ofan interlayer insulating material at a high rate. The lower limit of thepolishing rate for an insulating material (for example, silicon oxide)is preferably 350 nm/min or more, more preferably 400 nm/min or more,further preferably 450 nm/min or more, and particularly preferably 500nm/min or more.

The slurry and the polishing method of the present embodiment can alsobe used in polishing of a pre-metal insulating material. Examples of thepre-metal insulating material include silicon oxide, phosphorus-silicateglass, boron-phosphorus-silicate glass, silicon oxyfluoride, andfluorinated amorphous carbon.

The slurry and the polishing method of the present embodiment can alsobe applied to materials other than the insulating material such assilicon oxide. Examples of such a material include high permittivitymaterials such as Hf-based, Ti-based, and Ta-based oxides; semiconductormaterials such as silicon, amorphous silicon, SiC, SiGe, Ge, GaN, GaP,GaAs, and organic semiconductors; phase-change materials such as GeSbTe;inorganic electroconductive materials such as ITO; and polymer resinmaterials such as polyimide-based, polybenzooxazole-based, acrylic,epoxy-based, and phenol-based materials.

The slurry and the polishing method of the present embodiment can beapplied not only to film-like objects to be polished, but also tovarious types of substrates made of glass, silicon, SiC, SiGe, Ge, GaN,GaP, GaAs, sapphire, plastics, or the like.

The slurry and the polishing method of the present embodiment can beused not only for the production of semiconductor elements, but also forthe production of image display devices such as TFT or organic EL;optical components such as a photomask, a lens, a prism, an opticalfiber, or a single crystal scintillator; optical elements such as anoptical switching element or an optical waveguide; light-emittingelements such as a solid laser or a blue laser LED; and magnetic storagedevices such as a magnetic disc or a magnetic head.

According to the present embodiment, it is possible to provide a methodfor producing abrasive grains, the method including a step of bringingfirst particles containing cerium oxide into contact with secondparticles containing a cerium compound. According to the presentembodiment, it is possible to provide a method for producing a slurry,the method including a step of obtaining abrasive grains by the methodfor producing abrasive grains.

EXAMPLES

Hereinafter, the present invention will be specifically described basedon Examples; however, the present invention is not limited to thefollowing Examples.

<Preparation of Cerium Oxide Slurry>

Particles containing cerium oxide (first particles; hereinafter,referred to as “cerium oxide particles”) and trade name: ammoniumdihydrogen phosphate manufactured by Wako Pure Chemical Industries, Ltd.(molecular weight: 97.99) were mixed to prepare a cerium oxide slurry(pH: 7) containing 5.0% by mass (solid content amount) of the ceriumoxide particles. The mixing amount of the ammonium dihydrogen phosphatewas adjusted to 1% by mass on the basis of the total amount of thecerium oxide particles.

An adequate amount of the cerium oxide slurry was introduced into tradename: MICROTRAC MT3300EXII manufactured by MicrotracBEL Corp., and theaverage particle size of the cerium oxide particles was measured. Thedisplayed average particle size value was obtained as the averageparticle size (average secondary particle size). The average particlesize of the cerium oxide particles in the cerium oxide slurry was 145nm.

An adequate amount of the cerium oxide slurry was introduced into tradename: DelsaNano C manufactured by Beckman Coulter, Inc. and measurementwas performed twice at 25° C. The average value of the displayed zetapotentials was obtained as the zeta potential. The zeta potential of thecerium oxide particles in the cerium oxide slurry was −55 mV.

<Preparation of Cerium Hydroxide Slurry>

(Synthesis of Cerium Hydroxide)

480 g of an aqueous 50% by mass Ce(NH₄)₂(NO₃)₆ solution (trade name:CANSO liquid manufactured by Nihon Kagaku Sangyo Co., Ltd.) was mixedwith 7450 g of pure water to obtain a solution. Next, while thissolution was stirred, 750 g of an aqueous solution of imidazole (10% bymass aqueous solution, 1.47 mol/L) was added dropwise thereto at amixing rate of 5 mL/min, and thereby a precipitate containing ceriumhydroxide was obtained. The cerium hydroxide was synthesized at atemperature of 20° C. and a stirring speed of 500 min′ The stirring wasperformed using a 3-blade pitch paddle with a total blade section lengthof 5 cm.

The obtained precipitate (precipitate containing cerium hydroxide) wassubjected to centrifugal separation (4000 min′, for 5 minutes), and thensubjected to solid-liquid separation with removal of a liquid phase bydecantation. 10 g of the particles obtained by solid-liquid separationwere mixed with 990 g of water, and then the particles were dispersed inwater using an ultrasonic cleaner, thereby preparing a cerium hydroxideslurry (content of particles: 1.0% by mass) containing particles thatcontained cerium hydroxide (second particles; hereinafter, referred toas “cerium hydroxide particles”).

(Measurement of Average Particle Size)

When the average particle size (average secondary particle size) of thecerium hydroxide particles in the cerium hydroxide slurry was measuredusing trade name: N5 manufactured by Beckman Coulter, Inc., a value of10 nm was obtained. The measuring method was as follows. First, about 1mL of a measuring sample (cerium hydroxide slurry, aqueous dispersionliquid) containing 1.0% by mass of cerium hydroxide particles wasintroduced into a 1-cm square cell, and then the cell was placed in theN5. Measurement was performed at 25° C. with the refractive index set to1.333 and the viscosity set to 0.887 mPa·s as the measuring sampleinformation of N5 software, and the value displayed as Unimodal SizeMean was read off.

(Measurement of Zeta Potential)

An adequate amount of the cerium hydroxide slurry was introduced intotrade name: DelsaNano C manufactured by Beckman Coulter, Inc. andmeasurement was performed twice at 25° C. The average value of thedisplayed zeta potentials was obtained as the zeta potential. The zetapotential of the cerium hydroxide particles in the cerium hydroxideslurry was +50 mV.

(Structural Analysis of Cerium Hydroxide Particles)

An adequate amount of the cerium hydroxide slurry was taken andvacuum-dried to isolate the cerium hydroxide particles, and thensufficiently washed with pure water to obtain a sample. When theobtained sample was measured by FT-IR ATR method, a peak based onnitrate ion (NO₃ ⁻) was observed in addition to a peak based onhydroxide ion (OH). Furthermore, when the same sample was measured byXPS (N-XPS) for nitrogen, a peak based on nitrate ion was observed whileno peak based on NH₄+ was observed. These results confirmed that thecerium hydroxide particles at least partially contained particles havingnitrate ion bonded to a cerium element. Furthermore, since particleshaving hydroxide ion bonded to a cerium element were at least partiallycontained in the cerium hydroxide particles, it was confirmed that thecerium hydroxide particles contained cerium hydroxide. These resultsconfirmed that the cerium hydroxide contained a hydroxide ion bonded toa cerium element.

(Measurement of Absorbance and Light Transmittance)

An adequate amount of a cerium hydroxide slurry was taken and dilutedwith water such that the content of particles became 0.0065% by mass (65ppm), and thus, a measuring sample (aqueous dispersion liquid) wasobtained. About 4 mL of this measuring sample was introduced into a 1-cmsquare cell, and the cell was placed in a spectrophotometer (devicename: U3310) manufactured by Hitachi, Ltd. Measurement of the absorbancein a wavelength range of 200 to 600 nm was performed, and the absorbancefor light having a wavelength of 290 nm and the absorbance for a lighthaving a wavelength of 450 to 600 nm were measured. The absorbance forlight having a wavelength of 290 nm was 1.192, and the absorbance forlight having a wavelength of 450 to 600 nm was less than 0.010.

About 4 mL of a cerium hydroxide slurry (content of particles: 1.0% bymass) was introduced into a 1-cm square cell, and the cell was placed ina spectrophotometer (device name: U3310) manufactured by Hitachi, Ltd.Measurement of the absorbance in a wavelength range of 200 to 600 nm wasperformed, and the absorbance for light having a wavelength of 400 nmand the light transmittance for light having a wavelength of 500 nm weremeasured. The absorbance for light having a wavelength of 400 nm was2.25, and the light transmittance for light having a wavelength of 500nm was 92%/cm.

<Preparation of Slurry>

Example 1

While stirring at a rotation speed of 300 rpm using a stirring blade oftwo blades, 20 g of the cerium hydroxide slurry and 1940 g ofion-exchange water were mixed to obtain a mixed liquid. Subsequently,after mixing 40 g of the cerium oxide slurry in the mixed liquid whilestirring the mixed liquid, stirring was performed while being irradiatedwith ultrasonic waves using an ultrasonic cleaner (device name: US-105)manufactured by SND Co., Ltd. Thereby, a CMP slurry containing ceriumhydroxide particles (free particles) that were not in contact withcerium oxide particles in addition to composite particles includingcerium oxide particles and cerium hydroxide particles that were incontact with the cerium oxide particles (content of cerium oxideparticles: 0.1% by mass, content of cerium hydroxide particles: 0.01% bymass) was prepared.

Example 2

While stirring at a rotation speed of 300 rpm using a stirring blade oftwo blades, 25 g of the cerium hydroxide slurry and 1935 g ofion-exchange water were mixed to obtain a mixed liquid. Subsequently,after mixing 40 g of the cerium oxide slurry in the mixed liquid whilestirring the mixed liquid, stirring was performed while being irradiatedwith ultrasonic waves using an ultrasonic cleaner (device name: US-105)manufactured by SND Co., Ltd. Thereby, a CMP slurry containing ceriumhydroxide particles (free particles) that were not in contact withcerium oxide particles in addition to composite particles includingcerium oxide particles and cerium hydroxide particles that were incontact with the cerium oxide particles (content of cerium oxideparticles: 0.1% by mass, content of cerium hydroxide particles: 0.0125%by mass) was prepared.

Example 3

While stirring at a rotation speed of 300 rpm using a stirring blade oftwo blades, 30 g of the cerium hydroxide slurry and 1930 g ofion-exchange water were mixed to obtain a mixed liquid. Subsequently,after mixing 40 g of the cerium oxide slurry in the mixed liquid whilestirring the mixed liquid, stirring was performed while being irradiatedwith ultrasonic waves using an ultrasonic cleaner (device name: US-105)manufactured by SND Co., Ltd. Thereby, a CMP slurry containing ceriumhydroxide particles (free particles) that were not in contact withcerium oxide particles in addition to composite particles includingcerium oxide particles and cerium hydroxide particles that were incontact with the cerium oxide particles (content of cerium oxideparticles: 0.1% by mass, content of cerium hydroxide particles: 0.015%by mass) was prepared.

Example 4

While stirring at a rotation speed of 300 rpm using a stirring blade oftwo blades, 35 g of the cerium hydroxide slurry and 1925 g ofion-exchange water were mixed to obtain a mixed liquid. Subsequently,after mixing 40 g of the cerium oxide slurry in the mixed liquid whilestirring the mixed liquid, stirring was performed while being irradiatedwith ultrasonic waves using an ultrasonic cleaner (device name: US-105)manufactured by SND Co., Ltd. Thereby, a CMP slurry containing ceriumhydroxide particles (free particles) that were not in contact withcerium oxide particles in addition to composite particles includingcerium oxide particles and cerium hydroxide particles that were incontact with the cerium oxide particles (content of cerium oxideparticles: 0.1% by mass, content of cerium hydroxide particles: 0.0175%by mass) was prepared.

Example 5

While stirring at a rotation speed of 300 rpm using a stirring blade oftwo blades, 40 g of the cerium hydroxide slurry and 1920 g ofion-exchange water were mixed to obtain a mixed liquid. Subsequently,after mixing 40 g of the cerium oxide slurry in the mixed liquid whilestirring the mixed liquid, stirring was performed while being irradiatedwith ultrasonic waves using an ultrasonic cleaner (device name: US-105)manufactured by SND Co., Ltd. Thereby, a CMP slurry containing ceriumhydroxide particles (free particles) that were not in contact withcerium oxide particles in addition to composite particles includingcerium oxide particles and cerium hydroxide particles that were incontact with the cerium oxide particles (content of cerium oxideparticles: 0.1% by mass, content of cerium hydroxide particles: 0.02% bymass) was prepared.

Example 6

While stirring at a rotation speed of 300 rpm using a stirring blade oftwo blades, 50 g of the cerium hydroxide slurry and 1910 g ofion-exchange water were mixed to obtain a mixed liquid. Subsequently,after mixing 40 g of the cerium oxide slurry in the mixed liquid whilestirring the mixed liquid, stirring was performed while being irradiatedwith ultrasonic waves using an ultrasonic cleaner (device name: US-105)manufactured by SND Co., Ltd. Thereby, a CMP slurry containing ceriumhydroxide particles (free particles) that were not in contact withcerium oxide particles in addition to composite particles includingcerium oxide particles and cerium hydroxide particles that were incontact with the cerium oxide particles (content of cerium oxideparticles: 0.1% by mass, content of cerium hydroxide particles: 0.025%by mass) was prepared.

Example 7

While stirring at a rotation speed of 300 rpm using a stirring blade oftwo blades, 70 g of the cerium hydroxide slurry and 1890 g ofion-exchange water were mixed to obtain a mixed liquid. Subsequently,after mixing 40 g of the cerium oxide slurry in the mixed liquid whilestirring the mixed liquid, stirring was performed while being irradiatedwith ultrasonic waves using an ultrasonic cleaner (device name: US-105)manufactured by SND Co., Ltd. Thereby, a CMP slurry containing ceriumhydroxide particles (free particles) that were not in contact withcerium oxide particles in addition to composite particles includingcerium oxide particles and cerium hydroxide particles that were incontact with the cerium oxide particles (content of cerium oxideparticles: 0.1% by mass, content of cerium hydroxide particles: 0.035%by mass) was prepared.

Example 8

20 g of the cerium hydroxide slurry, 60 g of ion-exchange water, and 20g of the cerium oxide slurry were sequentially added to a 1-mm-diametercylindrical container containing zirconia beads to obtain a mixedliquid. Subsequently, the mixed liquid was placed on a mix rotormanufactured by AS ONE CORPORATION (device name: MR-5) and stirred at100 rpm. Thereafter, 900 g of ion-exchange water was added and thenstirred. Thereby, a CMP slurry containing cerium hydroxide particles(free particles) that were not in contact with cerium oxide particles inaddition to composite particles including cerium oxide particles andcerium hydroxide particles that were in contact with the cerium oxideparticles (content of cerium oxide particles: 0.1% by mass, content ofcerium hydroxide particles: 0.02% by mass) was prepared.

Example 9

25 g of the cerium hydroxide slurry, 55 g of ion-exchange water, and 20g of the cerium oxide slurry were sequentially added to a 1-mm-diametercylindrical container containing zirconia beads to obtain a mixedliquid. Subsequently, the mixed liquid was placed on a mix rotormanufactured by AS ONE CORPORATION (device name: MR-5) and stirred at100 rpm. Thereafter, 900 g of ion-exchange water was added and thenstirred. Thereby, a CMP slurry containing cerium hydroxide particles(free particles) that were not in contact with cerium oxide particles inaddition to composite particles including cerium oxide particles andcerium hydroxide particles that were in contact with the cerium oxideparticles (content of cerium oxide particles: 0.1% by mass, content ofcerium hydroxide particles: 0.025% by mass) was prepared.

Example 10

30 g of the cerium hydroxide slurry, 50 g of ion-exchange water, and 20g of the cerium oxide slurry were sequentially added to a 1-mm-diametercylindrical container containing zirconia beads to obtain a mixedliquid. Subsequently, the mixed liquid was placed on a mix rotormanufactured by AS ONE CORPORATION (device name: MR-5) and stirred at100 rpm. Thereafter, 900 g of ion-exchange water was added and thenstirred. Thereby, a CMP slurry containing cerium hydroxide particles(free particles) that were not in contact with cerium oxide particles inaddition to composite particles including cerium oxide particles andcerium hydroxide particles that were in contact with the cerium oxideparticles (content of cerium oxide particles: 0.1% by mass, content ofcerium hydroxide particles: 0.03% by mass) was prepared.

Comparative Example 1

After mixing 40 g of the cerium oxide slurry and 1960 g of ion-exchangewater while stirring the mixed liquid at a rotation speed of 300 rpmusing a stirring blade of two blades, stirring was performed while beingirradiated with ultrasonic waves using an ultrasonic cleaner (devicename: US-105) manufactured by SND Co., Ltd. Thereby, a CMP slurrycontaining cerium oxide particles (content of cerium oxide particles:0.1% by mass) was prepared.

Comparative Example 2

After mixing 200 g of the cerium hydroxide slurry and 1800 g ofion-exchange water while stirring the mixed liquid at a rotation speedof 300 rpm using a stirring blade of two blades, stirring was performedwhile being irradiated with ultrasonic waves using an ultrasonic cleaner(device name: US-105) manufactured by SND Co., Ltd. Thereby, a CMPslurry containing cerium hydroxide particles (content of ceriumhydroxide particles: 0.1% by mass) was prepared.

<pH of CMP Slurry>

The pH of each of the CMP slurries mentioned above was measured usingModel No. PHL-40 manufactured by DKK-TOA CORPORATION. The measurementresults are shown in Table 1.

<Average Particle Size of Abrasive Grains>

Each of the CMP slurries mentioned above was introduced in an adequateamount into trade name: MICROTRAC MT3300EXII manufactured byMicrotracBEL Corp., and measurement of the average particle size of theabrasive grains was performed. The displayed average particle size valuewas obtained as the average particle size (average secondary particlesize) of the abrasive grains. The measurement results are shown in Table1.

<Measurement of Absorbance of Supernatant Solution>

The content of the abrasive grains (the total amount of particles) inthe CMP slurry was adjusted to 0.1% by mass (for example, diluted withion-exchange water) to prepare a test liquid. 7.5 g of the test liquidwas introduced in a centrifugal separator (trade name: Optima MAX-TL)manufactured by Beckman Coulter, Inc. and treated at a centrifugalacceleration of 5.8×10⁴ G and at a setting temperature of 25° C. for 5minutes to obtain a supernatant solution.

About 4 mL of the supernatant solution was introduced into a 1-cm squarecell made of quartz, and then, the cell was placed in aspectrophotometer (device name: U3310) manufactured by Hitachi, Ltd.Measurement of the absorbance was performed in a wavelength range of 200to 600 nm, and a value of the absorbance in a wavelength of 380 nm wasread from a chart thus obtained. The measurement results are shown inTable 1. Further, as for Examples 1 to 10, a value of the lighttransmittance in a wavelength of 500 nm was read from the chart thusobtained, and as a result, the value was 92%/cm or more.

<CMP Evaluation>

The content of the abrasive grains (the total amount of particles) inthe CMP slurry was adjusted to 0.1% by mass (diluted with ion-exchangewater) to prepare a CMP polishing liquid. The substrate to be polishedwas polished by using this CMP polishing liquid under the polishingconditions below. Values of the pH in the CMP polishing liquid and theaverage particle size of the abrasive grains were the same as the valuesin the CMP slurry mentioned above.

[CMP Polishing Conditions]

Polishing apparatus: MIRRA (manufactured by Applied Materials, Inc.)

Flow rate of CMP polishing liquid: 200 mL/min

Substrate to be polished: As a blanket wafer having no pattern formedthereon, a substrate to be polished having a silicon oxide film having athickness of 2 μm, which had been formed by a plasma CVD method, on asilicon substrate was used.

Polishing pad: Foamed polyurethane resin having closed pores(manufactured by Dow Chemical Japan Ltd., Product No.: IC1010) Polishingpressure: 13 kPa (2.0 psi)

Rotation numbers of substrate to be polished and polishing platen:Substrate to be polished/polishing platen=93/87 rpm

Polishing time: 1 minute (60 seconds)

Washing of wafer: After a CMP treatment, washing was performed withwater while applying an ultrasonic wave, and then drying was performedwith a spin dryer.

The polishing rate for a silicon oxide film (SiO₂RR) that had beenpolished and washed under the above-described conditions was obtained bythe formula below. The results are shown in Table 1. The film thicknessdifference of the silicon oxide film before and after polishing wasobtained using a light interference type film thickness measuringapparatus (trade name: F80 manufactured by Filmetrics Japan, Inc.).Polishing rate (RR)=(Film thickness difference [nm] of silicon oxidefilm before and after polishing)/(Polishing time: 1[min])

TABLE 1 Compar- ative Example Example 1 2 3 4 5 6 7 8 9 10 1 2 Contentof Cerium oxide 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 — abrasiveparticles grains Cerium hydroxide 0.01 0.0125 0.015 0.0175 0.02 0.0250.035 0.02 0.025 0.035 — 0.1 [% by mass] particles pH of CMP slurry 4.13.9 3.9 4.0 4.1 4.3 4.5 4.1 4.3 4.4 7.0 4.0 Average particle size of 220155 155 155 155 155 155 155 155 155 145 10 abrasive grains [nm]Absorbance at 380 nm 0.002 0.032 0.068 0.083 0.093 0.164 0.239 0.1080.183 0.205 0 0.99 of supernatant solution Polishing rate for silicon355 360 401 450 456 548 530 460 532 527 245 28 oxide [nm/min]

The invention claimed is:
 1. A slurry comprising abrasive grains and aliquid medium, wherein the abrasive grains include first particles andsecond particles in contact with the first particles, a particle size ofthe second particles is smaller than a particle size of the firstparticles, the first particles contain cerium oxide, the secondparticles contain a cerium compound, and in a case where a content ofthe abrasive grains is 0.1% by mass, an absorbance for light having awavelength of 380 nm in a liquid phase obtained when the slurry issubjected to centrifugal separation for 5 minutes at a centrifugalacceleration of 5.8×10⁴ G exceeds
 0. 2. The slurry according to claim 1,wherein the cerium compound contains cerium hydroxide.
 3. The slurryaccording to claim 1, wherein a content of the abrasive grains is 0.01to 10% by mass.
 4. The slurry according to claim 1, wherein the slurryis used for polishing a surface to be polished containing silicon oxide.5. A polishing method comprising a step of polishing a surface to bepolished by using the slurry according to claim
 1. 6. The slurryaccording to claim 1, wherein a particle size of the first particles is100 nm or more.
 7. The slurry according to claim 1, wherein a particlesize of the second particles is 30 nm or less.
 8. The slurry accordingto claim 1, wherein an average particle size of the abrasive grains is120 nm or more.
 9. The slurry according to claim 1, wherein a content ofcerium oxide in the abrasive grains is 50 to 95% by mass on the basis ofthe entire abrasive grains.
 10. The slurry according to claim 1, whereina content of cerium hydroxide in the abrasive grains is 5 to 50% by masson the basis of the entire abrasive grains.
 11. The slurry according toclaim 1, wherein a content of the abrasive grains is 0.01 to 0.5% bymass.
 12. The slurry according to claim 1, wherein a light transmittancefor light having a wavelength of 500 nm in a liquid phase obtained whenthe slurry is subjected to centrifugal separation for 5 minutes at acentrifugal acceleration of 5.8×10⁴ G is 50%/cm or more.
 13. The slurryaccording to claim 1, wherein pH is 2.0 to 7.0.
 14. The slurry accordingto claim 1, wherein pH is 3.0 to 5.0.
 15. The polishing method accordingto claim 5, wherein the surface to be polished contains silicon oxide.